Aromatic alkylation



United States Patent AROMATIC ALKYLATION Earl Vance Kirkland, La Marque, Tex. assignor to The American Oil Company, a corporation of Texas No Drawing. Application May 13, 1954, Serial No. 429,680

4 Claims. (Cl. 260-671) This invention relates to the alkylation of aromatic hydrocarbons in the presence of a catalyst consisting of solid phosphoric acid promoted with BFa.

An object of the invention is the preparation of isopropylaromatic hydrocarbons by alkylating aromatic hydrocarbons with propylene in the presence of a catalyst consisting of solid phosphoric acid promoted with BFs. A particular object is the alkylation of aromatic hydrocarbons with propylene in the presence of solid phosphoric acid-B1 3 catalyst under conditions to improve catalyst life. The preferred object of the invention is the preparation of isopropylxylenes by alkylation of xylene with propylene in the presence of a solid phosphoric acid-B153 catalyst under conditions to give long catalyst life.

The invention concerns an alkylation process wherein an aromatic hydrocarbon is reacted at a constant pressure with propylene, in the presence of a catalyst consisting of solid phosphoric acid saturated with BFs; BFa is continuously introduced into the reaction zone during the period of contacting of the aromatic hydrocarbon and the propylene. A reaction product mixture is separated from the solid catalyst and isopropylaromatic hydrocarbons are recovered from the reaction product mixture.

The catalyst utilized in this process consists of a solid phosphoric acid saturated with BF 3. The solid phosphoric acid component of the catalyst may be the conventional solid phosphoric acid catalyst utilized for polymerization of refinery butylene streams; this commercial catalyst is commonly known as UOP polycatalyst. In general, the solid phosphoric acid consists of between about 50 and 75 weight percent of phosphoric acids such as orthophosphoric and pyrophosphoric acid. The acid is adsorbed on a carrier of a siliceous character. Examples of these carriers are diatomaceous earth, kieselguhr, silica gel, aluminum silicate, fullers earth, bentonite, and acid treated clays. The acid and the adsorbent are mixed together and usually extruded to form shaped particles. The shaped particles are then dried at a temperature of from about 350 to about 500 F. The dried particles are calcined further at temperatures generally from about 500 to about 1000" F. It is to be understood that all the various solid phosphoric acids known to the art are intended to be included within this description and the above description is not to be considered as limiting the type of solid phosphoric acid usable in the process of this invention.

The catalyst of this invention is prepared by exposing solid phosphoric acid to gaseous BFa at the desired temperature of alkylation until the solid phosphoric acid has become saturated with the BF3. The saturation point is most readily determined by the appearance of BF3 in the efliuent from the chamber containing the solid phosphoric acid.

The process involves the reaction of propylene with aromatic hydrocarbons. These may be either monocyclic or polycyclic, such as naphthalene, methylnaphthalene, anthracene. The monocyclic hydrocarbons may be either benzene or alkylbenzenes, such as toluene, ethylbenzene, xylene mesitylene and durene. Particularly good results are obtainable With the various Xylene isomers.

The process may be carried out at various temperatures. The aromatic hydrocarbon must be in the liquid state and therefore the operating temperature must be above the melting point of the particular aromatic hydrocarbon charged. In general, the process is carried out at temperatures between about 25 C. and 150 C. When operating with xylene as the feed, it is preferred to use a temperature between about 70 C. and C.

The process is carried out under conditions to maintain substantially constant pressure in the reaction zone. In batch operations, this constant pressure is readily maintained by venting some of the gaseous material from the reaction zone. In continuous operation, obviously the reaction zone will be at substantially constant pressure.

The amount of propylene utilized will be dependent upon the type of isopropylaromatic hydrocarbon desired. The molar ratio of propylene to aromatic hydrocarbon is not an essential feature of the process. However, it is preferred to maintain an external molar ratio of propylene to xylene of between about 0.1 and 2. The molar ratio isexpressed as external ratio because in batch operations wherein the propylene is introduced over a period of time, the total amount of propylene charged is much larger than the amount of propylene present in the reaction zone at any particular instant. Thus, external mol ratio is intended to mean the ratio of total amount of propylene charged to the reaction zone to the total amount of aromatic hydrocarbon charged.

When the solid phosphoric acid-BFa catalyst, i. e., a solid phosphoric acid saturated with BFa at operating temperature and pressure, is used to catalyze the reaction of aromatic hydrocarbon and propylene, the catalyst very rapidly loses its activity. In other words, the solid phosphoric acid-BFs catalyst has an extremely short life. The life of the catalyst is prolonged almost indefinitely when gaseous BFs is introduced continuously into the reaction zone during the course of the alkylation reaction. When propylene is introduced into the reaction zone more or less continuously, the BR; is introduced into the reaction zone during the time of propylene addition. In batch operations, wherein the total amount of aromatic hydrocarbon and propylene are introduced into the reaction zone in a single addition, improved results are obtained by adding BFa continuously to the reaction zone over the period of time required to obtain the desired consumption of propylene.

The amount of BFa introduced into the reaction zone during the alkylation reaction time will vary with the particular feed and the particular operating conditions. In general, the BFs addition rate is between about 0.02 and 0.1 mol per mol of aromatic hydrocarbon per hour of contacting time. When xylene is the feed, it is preferred to use about 0.05 mol of BFs per mol of xylene per hour of reaction time.

The alkylation reaction is not a rapid one and therefore sufficient time must be allowed in the reaction zone to obtain the desired amount of propylene reaction. The reaction time is known to be affected by the temperature, catalyst activity, the type of aromatic hydrocarbon, etc.

The results obtainable by the process of this invention are illustrated by the following examples, which examples are not to be construed as limiting the scope of the in vention.

The tests were carried out using a Pyrex glass reactor. The reactor was two inches in diameter and 30 inches overall length. Near the lower end of the reactor a coarse fritted glass disk was fused to the wall. This fritted glass disk acted as a distributor plate for the gas entering the reaction zone by way of a valved line below the glass disk. An entry point for a thermocouple was provided about 12 inches above the glass disk; Near the same rate as in Test 1 for a time of 2.5 hours. The results of this test are set out in Table I.

It is evident by the nearly doubled production of monoisopropylxylene that the solid phosphoric acid-BFs catathe top of the reaction chamber a fill point was provided. 5 y in conjunction With the introduction of BF3 is a Vastly A water-cooled condenser was connected to a gaseous Superior alkylatiefl catalyst than BFB aloneefiiuent outlet of the reaction chamber.

The solid phosphoric acid used in the tests was UOP TESTZS 3a 3b j No. 2 polymerization catalyst made up in one-quarter These tests were earned out 111 a {hamlet 51111-11211 to inch cylindrical pellets. This acid used kieselguhr as that of Test e P that the 11101 Tittle 0f P py to the support. Analysis indicated that the solid prosphoric Xylene was Varled- However, the tlme Tatlo was held acid contained about 5 f acid cakulated as Phosconstant in the two tests. The results of these tests are phorous pentoxide. The pellets were added to the reactor Presented 1h Table to form a bed about 14 inches high.

In each of the tests, 500 ml. of aromatic hydrocarbon 15 TESTS 4afl4d were added to the reactor; this amount completely covered In the e tests, the alkylation reaction was carried out the bed of solid phosphoric acid pellets. The pellets without introducing BFs into the reaction zone during and the xylene were heated to the desired reaction temthe course of the alkylation reaction. That is, the'solid perature and then the solid phosphoric acid was saturated phosphoric acid pellets and the xylene charged were with BFs by passing BFa into the reaction chamber at saturated with BF; according to the method described. a rate of about 80 ml. per minute. In all the tests, the In Test 4a, propylene was added to the reaction zone pressure in the reaction zone was atmospheric. The over a period of one hour without adding BFa; the saturation time was easily determined by the first appearreaction product mixture was drained from the reactor. ance of BFs in the efiiuent from the condenser. Although In Test 4b, fresh xylene was added to the reactor con- 2 the catalyst was saturated in about 5 minutes, the BFs taining the catalyst from Test 4a. Propylene was added was passed through the reactor for about minutes. for one hour and then the reaction product mixture Propylene was metered into the bottom of the reaction withdrawn. I Test 4c, fresh Xylene was added to the chamber below the fritted glass disk at a predetermined catalyst remaining from Test 4b and in Test 4d, fresh rate and the addition was continued for a predetermined xylene was added to the catalyst remaining from Test 40. 5 time. The. results obtained in each of these tests are shown in During those tests wherein BF3 was added to the re- Table I. 1

Table I 3 4' Test No 1 2 a b a b c1 11 Time, Hours 3 2.5 s 1 1 J 1 1. 'Temperature, C 75-80 75-80 75-30 75-80 75-80 75-80 75-80 '75-80' Total oslXylene, M01 Ratio" 0.7 0. 72 O. 31 0. 47 0.4 0.4 0. 4 0. 4 C /Xylene/Hr M01 Rat 0. 23 0. 20 0.16 0.16 0.4 0.4 0.4 0.4 Product, Wt. Percent of Xyl V Xylene (135150O.) 53.5 39 60 57.5 77.5 90.5 94 90.5 Isopropyl Xylene (NB-205C 29 55 24. 3 23. 5 17 0 0 0 Diisopropyl Xylene (THO-245 C.) 8 8 1.0 2. 1 0 0 0 0 Bottoms 9 7 3.4 3. 7 5 9. 5 0 3. 5

' action zone while the propylene was being added, the BR:

was metered into the line which introduced the propylene into the reactor so that the BFa and propylene entered the bottom of the reaction zone simultaneously.

At the end of the predetermined time, the reaction chamber was cooled to room temperature. The reaction product mixture consisting of unreacted aromatic hydrocarbon and alkylate and some propylenewas drained into a separator funnel and washed with dilute caustic and water to remove BFs. The neutral liquid was freed of water and fractionated through a 25 x 180 mm. glass column packed with metal saddles. Close boiling fractions were taken from the column and analyzed by physical characteristics and infrared spectrum.

TEST 1 In this test, xylene was treated with propylene in the absence of a solid phosphoric acid. The only catalyst was BFs. The xylene was charged to the empty reaction zone and saturated with BF3. Then the mixed stream of BF3, 80 ml. per minute, and propylene was added to the reactor for a time of three hours. The results of this test are set out in Table I.

TEST 2 In this test, the solid phosphoric acid-B1 3 catalyst V bon with propylene at a' temperature between about 25 C. and 150 C., in the presence of a catalyst consisting of solid phosphoric acid saturated with BFs, (b) continuously introducing BFa and said propylene into said contacting zone throughout the contacting time wherein I the rate of BF3 introduction is between 0.02 and 0.1

I moles per mole of said aromatic hydrocarbon per hour of contacting time, (c) separating reaction product mixture from said catalyst and (d) recovering isopropylaromatic hydrocarbons from said mixture.

2. The process of claim 1 wherein said solid phosphoric acid comprises phosphoric acid deposited on a siliceous was used. The reactor was charged with the catalyst and with xylene as'in the normal procedure described above. BR and propylene were introduced at about carrier.

3. The process of claim 1 wherein said aromatic is xylene.

4. An alkylation process which comprises (1) introducing into a reaction zone a catalyst consisting of solid phosphoric acid which has been saturated with BE; (2) introducing into said zone liquid xylene and propylene,

(3) introducing BFs into said zone concurrently with said propylene at a rate of about 0.05 moles of BFs per mole of xylene per hour and wherein the external molar ratio of propylene to Xylene is between about 0.1 and 2, (4) maintaining said zone at a temperature be- 5 tween about 70 and 100 C. at a constant pressure sufiicient to maintain said xylene in the liquid state for a time sufiicient to obtain the desired propylene consumption, (5) withdrawing a reaction product mixture from said zone and (6) recovering isopropyl-xylenes 10 from said mixture.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ALKYLATION PROCESS WHICH COMPRISES (A) CONTACTING, AT CONSTANT PRESSURE, A LIQUID AROMATIC HYDROCARBON WITH PROPYLENE AT A TEMPERATURE BETWEEN ABOUT 25* C. AND 150* C., IN THE PRESENCE OF A CATALYST CONSISTING OF SOLID PHOSPHORIC ACID SATURATED WITH BF3, (B) CONTINUOUSLY INTRODUCING BF3 AND SAID PROPYLENE INTO SAID CONTACTING ZONE THROUGHOUT THE CONTACTING TIME WHEREIN THE RATE OF BF3 INTRODUCTION IS BETWEEN 0.02 AND 0.1 MOLES PER MOLE OF SAID AROMATIC HYDROCARBON PER HOUR OF CONTACTING TIME, (C) SEPARATING REACTION PRODUCT MIXTURE FROM SAID CATALYST AND (D) RECOVERING ISOPROPYLAROMATIC HYDROCARBONS FROM SAID MIXTURE. 